1. Field of the Invention
The present invention relates to an air filter, and more specifically to an air filter assembly for both mechanically and electrostatically filtering dust and other particulate matter from air.
2. Description of the Related Art
For a variety of health and cleanliness reasons, it is desirable to filter dust, pollen, and other particulate matter from air in residential and commercial buildings. This is commonly done by flowing air in a ventilation system through a filter assembly. Dust is removed mechanically or electrostatically by the filter.
Conventional air filters are either expensive or inefficient at removing dust from air. Disposable fiberglass or polypropylene air filters act to mechanically filter only a fraction of the amount of dust in the air of a building. In some instances, the filters include a resinous dust-retentive coating. However, dust still remains in the air after using such coated filters.
To improve filtering effectiveness, filters have been developed which perform both mechanical and electrostatic filtering. In an electrostatic filter assembly, a filter layer may include a pair of metallic grids, to which opposite electrostatic changes are applied by an external voltage source. Dust particles acquire the electrostatic charge of the first grid and adhere to the second oppositely-charged grid. This type of air filter is more effective than the simple mechanical filter. However, the electric components and the need for an external voltage source substantially increase the complexity and cost of the filter.
Other arrangements have been developed which filter air both mechanically and electrostatically without the application of electricity from an external source. However, such arrangements have been expensive to produce and have other shortcomings as well.